L0301P11 - Primary Tissue Types - Epithelium, Glands and Connective Tissue
Function of Cells *synthesis and secretion of: **enzymes **mucus **steroid hormones **protein hormones **acid **collagen **antibodies/immunoglobulins **absorption *contraction *generation and transmission of electrical impulses *movement of ions against a gradient *detection of foreign cells, structures *propulsion of mucus *formation of specialised barriers *storage of half the number of chromosomes *proliferation *Cells form Tissues which form Organs ∴ organs contain tissue of all 4 types Tissue *a coherent grouping of cells bound together by cell junctions or extracellular matrix (ECM) *each type of primary tissue is specialised for a particular function and has a distinct pattern of organisation Primary Tissue Types *epithelium *muscle **skeletal **cardiac **smooth nervous *central - CNS *peripheral - PNS connective *tendon, ligament *capsule *lamina propria *bone *cartilage *fat *blood Epithelium *the tissue that forms the surfaces of the body *external surfaces: **skin - epidermis *internal surfaces: lining of: **gastrointestinal tract **reproductive tract **urinary tract **respiratory tract **cardiovascular system ***from capillaries, arteries to heart chambers ***endothelium - lining of the inside of vessels Characteristics *very little space between cells *strong attachments between cells - intercellular junctions *sits on the basal lamina *have an orientation (top/bottom) - polarised *avascular - lack of blood vessels Functions *structure and function of epithelium varies from site to site: **protection - e.g. skin **absorption - e.g. small intestine, kidney **secretion - e.g. small intestine, trachea **transport - e.g. kidney **sensory perception - e.g. epidermis Characterisation *number of cell layers **simple = 1 **stratified > 1 *shape of most superficial cell **squamous - flat **cuboidal **columnar Types *simple squamous *simple cuboidal - glands, kidney *simple columnar - small intestine *stratified squamous - buccal cavity, tongue, oral cavity, vagina *keratinised stratified squamous - epidermis *stratified cuboidal *stratified columnar *transitional (urinary tract only) *pseudo-stratified **looks like multiple layers but is only one   Surface Specialisations Apical Surface *top or luminal Microvilli *the brush border) *most cells only have a few *some cells have hundreds or even thousands **e.g. absorptive cells of small intestine and kidney *amplify the surface area *about 1μm long *contain actin filaments   Cilia *elongated motile structures found in: **respiratory tract – propel mucus **oviduct - propel sperm and ovum **tracheal epithelial cells - 300 cilia each *beat 22 times per second *synchronised beating *10μm long *made up of microtubules: 9 pairs + 2 *basal body - protein structure at the base *require ATP ---- Basal Surface *bottom Hemidesmosome *similar to desmosomes *but attach one cell to the extracellular matrix *found at inner basal surface of keratinocytes in the epidermis of skin *refer image below - No.5 ---- Lateral Surface *side 1. Zonula Occludens *also known as tight junction *the most apical junction *zonula = band *completely encircles the cell *provides a seal that prevents the flow of material between cells in either direction *occludes the intercellular space *outer leaflets of the adjacent plasma membranes fuse   2. Zonula Adherens *encircles the cell *provides mechanical adhesion *specific glycoprotein – A-CAM in cleft *actin filaments insert into dense plaques on the cytoplasmic surfaces *plaques contain myosin, tropomyosin etc.   3. Macula Adherens *a.k.a desmosome, spot junctions *plaque-like thickenings on membranes of adjacent cells *thin dense line in middle of intercellular space *cytokeratin intermediate filaments converge on plaques to provide attachment *sites of attachment between cells and for cytoskeleton   4. Gap Junction *also known as nexus *close apposition of adjacent cell membranes *adjacent membranes do not fuse *intramembranous particles *consist of 6 sub- units arranged around a central pore (1.5nm diameter) *particles attach to particles in membrane of adjacent cell *joined particles called connexons *create a pore for ion flow (electrical coupling) between cells *for molecules up to MW 1200 *found in smooth and cardiac muscle cells ---- Basal Laminar *also known as the basement membrane *all epithelial layers rest upon this basement membrane *non cellular material made of: **collagen type IV **proteoglycans ***e.g. heparin sulphate proteoglycans (HSPGs) **glycoproteins ***fibronectin, laminin *not inert Function *provides adhesion *influences orientation and shape of cells *special junction - binds to the basal plasma membrane *sequesters growth factors *cannot be passed by normal epithelial cells - cancer cells do Connective Tissue *a supporting tissue that **forms the architectural framework for organs and cells **provides a dynamic extracellular environment Types Dense Connective Tissue *extracellular (non-living) components predominate *closely packed *relatively inflexible Regular *fibres randomly orientated *enables tissue to withstand tension from different directions *found deep to epithelia *e.g. dermis, organ capsules Irregular *regular or parallel arrangement of fibre bundles *maximum strength in one direction *e.g. tendons, ligaments Loose Connective Tissue *flexible and deformable *widely distributed *supports or envelopes many epithelial tissues, glands, muscles and nerves Areolar *very common *collagen fibres are loosely arranged *open (areolar) spaces between the collagen fibres are filled with ground substance Adipose *consists of adipose cells which synthesise and store fat Reticular *consists of reticular fibres forming a delicate supporting framework for cells Proteoglycans *fills the space between cells and fibres *bottlebrush shapes *consist of a protein core and GAGs on the sides *mainly carbohydrate (80-90% of the weight) *strong net negative charge *binds to many cations (usually Na+) *intensely hydrated (most water is bound) ---- Cell Types *loosely connected unlike epithelium *fibroblast **produce and maintain extracellular ground substance and fibres *macrophage **phagocytose foreign matter *mast cell **secrete histamine, heparin and cell attracting factors involved in the inflammatory response *plasma cell **derived from B lymphocytes *adipose cell (fat cell) **storage and metabolism of fat *chondroblast, chondrocyte **produce cartilage *osteoblast, osteoclast, osteocyte **produce and maintain bone *mesenchymal cells **embryonic stem cells which upon stimulation differentiate into adult connective tissue cells *blood cells: **e.g. lymphocytes, monocytes Extracellular Matrix Fibres *collagen **more than 20 known types **most common - type I **makes 30% of body’s total protein **high tensile strength **strong and inelastic - resistance to tear, stretch and provides integrity **produced mainly by fibroblasts *elastin **consists of fibrillin and elastin **provides elasticity **arterial walls, dermis, lung alveoli **synthesised by fibroblasts, smooth muscle cells and chondrocytes *reticular **same as type III collagen **mesh-like delicate framework **allows adherence and attachment of surrounding cells **glands, smooth muscle, blood vessels, lymphoid organs Ground Substance *proteoglycans *glycosaminoglycans (GAGs) *glycoproteins - fibronectin, laminin *water, electrolytes, hormones, gases